3 ms·

Refutation of the Walker study which "assesses the extent to which the sample size in the original analysis may have contributed to spurious results". https://

• ndsipa_pomu 4y ago
  Response to the refutation: https://researchportal.bath.ac.uk/en/publications/bicycle-helmet-wearing-is-associated-with-closer-overtaking-by-dr https://researchportal.bath.ac.uk/en/publications/bicycle-he... Olivier and Walter re-analysed the same data in 2013 and claimed helmet wearing was not associated with close vehicle passing. Here we show how Olivier and Walter’s analysis addressed a subtly, but importantly, different question than Walker’s. Their conclusion was based on omitting information about variability in driver behaviour and instead dividing overtakes into two binary categories of ‘close’ and ‘not close’; we demonstrate that they did not justify or address the implications of this choice, did not have sufficient statistical power for their approach, and moreover show that slightly adjusting their definition of ‘close’ would reverse their conclusions. We then present a new analysis of the original dataset, measuring directly the extent to which drivers changed their behaviour in response to helmet wearing. This analysis confirms that drivers did, overall, get closer when the rider wore a helmet.
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